xref: /freebsd/lib/libsys/mlockall.2 (revision 8269e7673cf033aba67dab8264fe719920c70f87)

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.\" by Jason R. Thorpe of the Numerical Aerospace Simulation Facility,
.\" NASA Ames Research Center.
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.Dd May 13, 2019
.Dt MLOCKALL 2
.Os
.Sh NAME
.Nm mlockall ,
.Nm munlockall
.Nd lock (unlock) the address space of a process
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/mman.h
.Ft int
.Fn mlockall "int flags"
.Ft int
.Fn munlockall "void"
.Sh DESCRIPTION
The
.Fn mlockall
system call locks into memory the physical pages associated with the
address space of a process until the address space is unlocked, the
process exits, or execs another program image.
.Pp
The following flags affect the behavior of
.Fn mlockall :
.Bl -tag -width ".Dv MCL_CURRENT"
.It Dv MCL_CURRENT
Lock all pages currently mapped into the process's address space.
.It Dv MCL_FUTURE
Lock all pages mapped into the process's address space in the future,
at the time the mapping is established.
Note that this may cause future mappings to fail if those mappings
cause resource limits to be exceeded.
.El
.Pp
Since physical memory is a potentially scarce resource, processes are
limited in how much they can lock down.
A single process can lock the minimum of a system-wide
.Dq wired pages
limit
.Va vm.max_user_wired
and the per-process
.Dv RLIMIT_MEMLOCK
resource limit.
.Pp
If
.Va security.bsd.unprivileged_mlock
is set to 0 these calls are only available to the super-user.
If
.Va vm.old_mlock
is set to 1 the per-process
.Dv RLIMIT_MEMLOCK
resource limit will not be applied for
.Fn mlockall
calls.
.Pp
The
.Fn munlockall
call unlocks any locked memory regions in the process address space.
Any regions mapped after an
.Fn munlockall
call will not be locked.
.Sh RETURN VALUES
A return value of 0 indicates that the call
succeeded and all pages in the range have either been locked or unlocked.
A return value of \-1 indicates an error occurred and the locked
status of all pages in the range remains unchanged.
In this case, the global location
.Va errno
is set to indicate the error.
.Sh ERRORS
.Fn mlockall
will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa flags
argument is zero, or includes unimplemented flags.
.It Bq Er ENOMEM
Locking the indicated range would exceed either the system or per-process
limit for locked memory.
.It Bq Er EAGAIN
Some or all of the memory mapped into the process's address space
could not be locked when the call was made.
.It Bq Er EPERM
The calling process does not have the appropriate privilege to perform
the requested operation.
.El
.Sh SEE ALSO
.Xr mincore 2 ,
.Xr mlock 2 ,
.Xr mmap 2 ,
.Xr munmap 2 ,
.Xr setrlimit 2
.Sh STANDARDS
The
.Fn mlockall
and
.Fn munlockall
functions are believed to conform to
.St -p1003.1-2001 .
.Sh HISTORY
The
.Fn mlockall
and
.Fn munlockall
functions first appeared in
.Fx 5.1 .
.Sh BUGS
The per-process and system-wide resource limits of locked memory apply
to the amount of virtual memory locked, not the amount of locked physical
pages.
Hence two distinct locked mappings of the same physical page counts as
2 pages aginst the system limit, and also against the per-process limit
if both mappings belong to the same physical map.